The influence of the protease inhibitor aprotinin on tumor invasion of three cell lines in vitro.

The production of protease by malignant cells has been held responsible for invasion. The effect of aprotinin, a broad-spectrum protease inhibitor, on malignant invasion was examined histologically in organotypical cocultures of precultured embryonic chick heart fragments with two human melanoma cell lines and one virus-transformed fetal mouse carcass cell line. In the presence of 400 KIU/ml aprotinin, invasion was still permissive, while in the comparison with 0.1 microgram/ml vincristine, a microtubule and directional motility inhibitor and a well-documented anti-invasive agent, invasion was completely stopped. Aprotinin remained stable in the culture medium so that the presence of invasion cannot be explained by low drug concentration. It is concluded that aprotinin-sensitive proteases are not implicated in invasion in vitro in the cell types investigated, and that this in vitro technique deserves further interest for the study of protease inhibitors in the mechanism of invasion.